It’s not uncommon to find painted parts with one matte side and one glossy side. This difference in finish is usually caused by factors related to the painting process, material application, or environmental conditions. Below is a simple breakdown of the main reasons:
Differences in Drying and Curing Conditions
Paint finish is highly affected by how it dries and cures. If one side of the part is exposed to higher temperature, better ventilation, or longer curing time, it will dry more evenly and form a glossy surface. The other side, if in a cooler, less ventilated area (e.g., shaded by the part itself or nearby objects), may dry slowly or incompletely. Slow drying can lead to uneven evaporation of solvents in the paint, resulting in a dull, matte finish.
This situation is particularly evident when curing parts in a tunnel oven. Especially when using semi-matte paint without hanging the parts or applying a full spray, the issue becomes more pronounced.
To avoid this issue, it is best to use custom hangers or switch to a convection oven. This is especially important for large parts or hardware components with hollow structures, where the right method must be selected.
Environmental Factors During Painting
Environmental conditions like humidity and air flow can also cause uneven finishes. High humidity during painting can affect solvent evaporation: one side of the part exposed to dry air may dry glossily, while the side in humid air may absorb moisture, leading to a matte or hazy finish. Similarly, uneven air flow (e.g., one side hit by direct wind) can speed up drying on that side, creating a different finish from the sheltered side.
In summary, the matte-glossy difference is mostly a result of inconsistencies in the painting process. Ensuring uniform surface preparation, consistent paint application, and stable drying/curing conditions can help avoid this issue.
Surface Preparation Discrepancies
Proper surface preparation (such as sanding, cleaning, or priming) is key to a uniform finish. If one side of the part is not sanded smoothly, or if there is dust, oil, or debris left on the surface before painting, the paint will not adhere evenly. A rough or contaminated surface disrupts the paint’s ability to form a smooth layer, leading to a matte finish. Meanwhile, a well-sanded and clean side allows the paint to spread evenly, creating a glossy effect.